Circuit interrupter having an improved tripping mechanism with an adjusting structure that cooperates with a bimetal to enhance tripping movement



Oct. 12, 1965 G. J. FREESE 3,211,861

CIRCUIT INTERRUPTER HAVING AN IMPROVED TRIPPING MECHANISM WITH AN ADJUSTING STRUCTURE THAT COOPERATES WITH A BIMETAL TO ENHANCE TRIPPING MOVEMENT Filed Nov. 15, 1961 2 Sheets-Sheet 1 WITNESSES INVENTOR Gerald J. Freese AT TORNE Y Oct. 12, 1965 G. J. FREESE 3,211,861

CIRCUIT INTERRUPTER HAVING AN IMPROVED TRIPPING MECHANISM WITH AN ADJUSTING STRUCTURE THAT COOPERATES WITH A BIMETAL To ENHANCE TRIPPING MOVEMENT Filed Nov. 15, 1961 2 Sheets-Sheet 2 85 I07 ll? 23 23 United States Patent 3,211,861 CIRCUIT INTERRUPTER HAVING AN IMPROVED TRIPPING MECHANISM WITH AN ADJUSTING STRUCTURE THAT COOPERATES WITH A BI- METAL TO ENHANCE TRIPPING MOVEMENT Gerald J. Freese, Brighton Township, Beaver County, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 15, 1961, Ser. No. 152,394 6 Claims. (Cl. 200-116) This invention relates to circuit interrupters, and more particularly to manually and automatically operable circuit breakers for controlling motor, lighting and other small and moderate power electric circuits.

Certain features that are herein disclosed are disclosed and claimed in the copending application of John N. Groves and Harold E. Reichert, Serial No. 142,395, filed November 15, 1961, and assigned to the assignee of the instant application.

An object of this invention is to provide a circuit breaker having improved means for unlatching a releasable member to effect automatic opening of the breaker contacts.

A further object of this invention is to provide a circuit breaker having an improved tripping mechanism comprising an adjusting structure that cooperates with a bimetal structure to enhance the tripping movement of the bimetal structure.

A further object of this invention is to provide a circuit breaker having a tripping mechanism comprising a bimetal structure with improved means for compensating for thermal reaction of the bimetal structure in response to changes in ambient temperature.

A general object of this invention is to provide a cira cuit breaker having increased utility.

The novel features that are considered characteristic of this invention are set forth in particular in the appended claims. The invention itself, both as to construction and operation, together with additional objects and advantages thereof, will be best understood from the following detailed description, when read in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a top plan view of a circuit breaker constructed in accordance with this invention;

FIG. 2 is a view taken along the line IIII of FIG. 1 looking in the direction of the arrows and showing the operating and tripping mechanisms of the circuit breaker;

FIG. 3 is a view taken along the line III-III of FIG. 1 looking in the direction of the arrows and showing the contact structure of one pole of the breaker;

FIG. 4 is a view taken along the line IV-IV of FIG. 1 looking in the direction of the arrows and showing the other pole of the breaker;

FIG. 5 is a front elevational view of the bimetal member seen in FIG. 2; and

FIG. 6 is an elevational view of part of the tripping mechanism of a different embodiment of the invention.

As shown in the drawings, a circuit breaker 3 comprises a housing 5 (FIG. 1) which is divided into four parts 7, 9, 11 and 13 to facilitate assembly of the breaker. The housing parts are all of molded insulating material.

The two central housing parts 9 and 11 are provided with internal surfaces and recesses for receiving and supporting a circuit-breaker mechanism 14 (FIG. 2) comprising an operating mechanism 15, a trip device 17 and a lighting device 19. The two central housing parts 9 and 11 are also provided with recesses and surfaces on the outer sides thereof that cooperate with similar recesses and surfaces on the inner sides of the outer housing parts 7 and 13 (FIG. 1) to receive and support the terminals,

3,211,861 Patented Oct. 12, 1965 conductors and contact structures seen in FIGS. 3 and 4. The parts 7, 9, 11 and 13 of the housing are held rigidly together by means of three rivets 21.

In order to mount the circuit breaker in an outlet box, there is provided a pair of brackets 23, one disposed at each end of the breaker housing. Each of the brackets 23 is provided with a pair of downwardly extending ears 25 (FIG. 2) having openings therein for receiving one of the rivets 21. The brackets 23 have openings 27 there in for receiving means for mounting the breaker on a panel.

As seen in FIG. 3, the various recesses and surfaces of the housing parts 7 and 9 support a pole unit comprising a conductor 29 having a solderless terminal connector 31 secured to one end thereof and a stationary contact 33 secured to the other end; a conductor 35 having a stationary contact 37 secured to one end thereof and a contact surface 39 at the other end and a conductor 41 having a contact surface 43 at one end thereof and a solderless terminal connector 45 suitably supported at the other end.

In operation, the stationary contacts 33 and 37 are bridged by a movable contact member 47 comprising a generally flat conducting plate 48 having two contact surfaces 49 at one end thereof. The plate 48 may be of a suitable conducting material such as copper and the contact surfaces 49 may be of a better conducting material such as silver. The contact plate 48 has a slot 51 therein for receiving a pin 53 that drives the member 47 to slide it endwise or rectilinearily in its plane into and out of engagement with the contacts 33, 37 in a manner to be hereinafter specifically described. As seen in FIG. 3, the housing part 9 has two surfaces 55 thereon that provide a track for guiding the member 47 in its path, The upper and lower surfaces 57 of the contact member 47 are curved as seen in FIG. 3 so that, if the contacts 49 or the contacts 33, 37 are slightly out of alignment, the contact member 47 can rock in the plane of its flat surfaces in order to provide adequate contact engagement.

When the movable contact member 47 is in the closed position, the circuit through the pole unit seen in FIG. 3 extends from the terminal 45 through the conductor 41, the contact 43, a plug-in type heater member indicated generally at 61 (FIG. 2), the contact 39 (FIG. 3), the conductor 35, the contact 37, the bridging movable contact member 47, the contact 33, the conductor 29 to the terminal member 31. The circuit is opened by movement of the contact member 47 to the open-circuit position seen in FIG. 3.

The various recesses and surfaces of the housing parts 11 and 13 (FIG. 1), support another pole unit (FIG. 4) comprising a conductor 63 having a solderless terminal connector 65 attached to one end thereof and a stationary contact 67 secured to the other end, and a conductor 69 having a solderless terminal connector 71 attached to one end thereof and a stationary contact 73 secured to the other end. Surfaces 75 on the housing part 11 form a track for guiding a contact member 47 that is identical with the contact member 47 seen in FIG. 3 for which reason like reference characters are applied to the con tact member seen in FIG. 4 except that the reference characters are primed in FIG. 4. A pin 53' is disposed in the slot 51' of the contact member 47 to move the contact member into and out of bridging contact engagement with the stationary contacts 67, 73 in the same manner as the contact member 47 is moved.

The circuit through the pole seen in FIG. 4 extends from the terminal 65 through the conductor 63, the contact 67, the movable contact member 47', the contact 73, the conductor 69 to the solderless terminal connector 71.

The contact members 47 and 47 are manually operated to the open and closed positions by operation of the operating mechanism 15 (FIG. 2) which comprises a handleoperating structure 77, an insulating contact operating arm 79, a releasable member 81 and an overcenter spring 83. The handle operating structure 77 is of molded insulating material and comprises a lever part 85 pivotally supported on two pins 87 (only one being shown in .FIG. 2) that are molded integral with the part 85. The pins 87 are pivotally supported in suitable openings in the molded housing parts 9 and 11. The lever part 85 of the operating structure 77 has an opening therein that is shaped to receive a handle part 89 having two extended parts 91 that fit into the opening. Thus, when it is desired to operate the operating structure 77, the handle 89 is placed in position providing leverage for operating the lever part 85, and, after operation, the operator can remove the'handle part 89 to make it difficult for an unauthorized person to manually operate the circuit breaker.

The operating lever 85 is generally U-shaped, only one leg 93 thereof being seen in FIG. 2. Each of the legs 93 is itself generally U-shaped as seen in FIG. 2 and each generally U-shaped leg 93 receives in the opening between its legs a pin 95 that is molded integral with the contact operating arm 79. The contact operating arm 79 is generally U-shaped (only one leg being seen in FIG. 2) and each leg thereof carries one of the pins 95 that is disposed in the opening between the legs of one of the U-shaped legs 93. An overcenter spring 83 is connected at oneend to the bight part of the U-shaped contact operating arm 79 and at the other end in a suitable depression in the releasable member 81. The releasable member 81 is pivotally supported by means of a pivot pin 97 that is rotatably seated in suitable openings in the housing parts 9 and 11. The outer or free end 99 of the releasable member 81 is latched in an opening 100 (FIG. in a bimetal member 101. Each of the pins 53 and 53' (FIGS. 3 and 4) is molded integral with one of the legs of the U-shaped contact operating arm 79 (FIG. 2) and is disposed in the associated slots 51 or 51' (FIGS. 3 and 4) in the associated movable contact member 47 or 47'.

The circuit breaker is shown in the open circuit position in FIGS. 1-4. Although at first glance the movable contact members 47 and 47' (FIGS. 3 and 4) appear to move in different directions, it will be understood from noticing the section lines and the direction of the arrows in FIG. 1 that these members 47 and 47' move in the same direction during operation.

When it is desired to close the circuit breaker, the handle portion 89 is rotated counterclockwise (FIG. 2) from the ofi to the on position. This movement,

because of the engagement of the U-shaped legs 93 of.

the operating lever 85 with the pins 95 of the contact operating member 79, and also because of the engagement of the pins 53 and 53' in the notches 51 and 51 of the contact members 47 and 47, moves the contact operating arm 79 down (the members 47 and 47' being prevented from moving back by engagement thereof with surfaces 103 and 103 that are formed on the housing members 9 and 11) charging the over-center spring 83. During this motion, the line of action of the over-center spring 83 is moved to the left of a straight line drawn between the centers of the pins 53, 95and 87, whereupon the over-center spring 83 discharges snapping the lower part of the movable contact arm 79 to the left (FIG. 2) moving the pins 53 and 53' to the left to rapidly move the movable contacts 47 and 47' into engagement with their respective stationary contacts 33, 37 and 67, 73.

Thereafter, in order to open the circuit interrupter, the handle portion 89 is manually rotated from the on to the off position (FIG. 2) during which movement the line of action of the over-center spring 83 is moved to the right of a straight line through the centers of the pins 53, 95 and 87, whereupon the spring 83 discharges snapping the movable contact arm 79 back to the position seen in FIG. 2, which movement, by virtue of the engagement of the pins 53 and 53' in the slots 51 and 51 of the contact members 47 and 47' (FIGS. 3 and 4), moves the movable contact members 47 and 47 back to the open-circuit position seen in FIGS. 3 and 4 with a snap-action.

The circuit breaker 3 is automatically tripped open.

upon the occurrence of an overload current condition above a predetermined amount by means of the trip device 17 (FIG. 2) comprising the plug-in heater member 61, the bimetal member 101, a calibrating and adjusting screw 105 and an adjusting member 107. Thebimetal member 101 is welded or otherwise secured to an L-shaped bracket 109 that is suitably secured to the housing parts 9 and 11. The bimetal member 101 has an opening (FIG. 5 therein forming a lower ledge 110 upon which one end 99 (FIG. 2) of the releasable member 81 is latched. The bimetal member 101 comprises a part 111 having a par-t 112 lanced out near the upper end thereof. As seen in FIG. 2, the lanced-out part 112 extends generally normal to the part 111. The calibrating screw is supported in a tapped opening in one leg of the bracket 109 and it engages the lanced-out part 112 of the bimetal 101. The upper end of the screw 105 has a notch 113 therein for receiving a screwdriver or other tool.

The plug-in heater member 61 (FIG. 2) is more specifically described in the aforementioned copending application of John N. Groves and Howard E. Reichert, Serial No. 152,395, filed November 15, 1961. This plugin heater member 61 comprises a supporting frame 117 of molded insulating material having'secured thereto two conducting plates 119 and 121. A resistance wire 123 is secured at one end to the conducting plate .119 and at the other end to the conducting plate 121. An insulating sheet 129 is provided between the resistance wire 123 and the conducting plates 119, 121, except where the connections 123, 127 are made. When the heater 61 is in position, a lower contact portion 131 of the conducting plate 119 engages the contact 39 (FIG. 3) of the con ductor 35, and an upper contact portion 133 (FIG. 2) on the conducting plate 121, engages the upper contact portion 43 (FIG. 3) of the conductor 41. When the plug-in heater 61 is in position, the circuit through the pole seen in FIG. 3 extends from the contact 39 through the contact 131 (FIG. 2), the conducting plate 119, the

resistance wire 123, the conducting plate 121, the contact 133, to the contact 43 (FIG. 3).

The high expansion side of the bimetal part 111 of the bimetal 101 is on the left as seen in FIG. 2 and the high expansion side of the bimetal part 112 is on the lower side of the part 112 as seen in FIG. 2. When the circuit breaker 3 is closed and an overload current condition above a predetermined amount occurs in the circuit controlled by the breaker, the resistance wire 123 of the plug-in heater member 61 is heated to inductively heat the bimetal structure 101 (FIG. 2). When the bimetal structure 101 is heated sufliciently, the part 111 thereof flexes so that the free or lower end thereof moves to the right (FIG. 2) to release or unlatch the releasable member 81. This tripping movement of the bimetal structure 101 is enhanced by the fact that the bimetal part 112 is also heated and it flexes so that its free end (to the left as seen in FIG. 2) moves upward exerting a bias against the screw 105 to enhance the tripping or releasing movement "of the bimetal structure 101. The screw 105 is moved only when the breaker is being calibrated or adjusted. During a tripping operation of the breaker, the screw 105 is stationary.

When the releasable member 81 is released, the overcenter spring 83 operates to pivot the member 81 clockwise about the pivot 97 moving the lever 85, the contact operating arm 79, and the over-center spring 83 to positions wherein the line of action of the spring 83 is to the right of a straight line through the centers of the pins 53, 95 and 87, whereupon the spring 83 operates to move the contact operating arm 79 to thereby move the contacts 47 and 47 to the open or tripped open position with a snap action. During this movement, the lever 85 and the handle part 89 are moved to a center position intermediate the on and off positions to provide a visual indication that the circuit breaker has tripped open.

After a tripping operation, the breaker is relatched by movement of the handle 89 and lever 85 to the extreme off position during which movement a part 137 of the lever 85 engages a pin 139 on the releasable member 81 to move the releasable member 81 counterclockwise about the pivot 97 to relatch the end 99 of the releasable member on the ledge 110 (FIG. 5) of the bimetal 101. Thereafter, the circuit breaker is manually operated in the same manner hereinbefore described by movement of the handle 89.

The circuit breaker is calibrated when it is assembled at the factory. This calibrating operation comprises running a predetermined overload current through the break- ,er and rotating the screw 105 to vary the amount of latching engagement between the end 99 of the releasable member 81 and the latching surface 110 of the bimetal 101 until the circuit breaker trips with the desired time delay being considered in the calibrating operation. Thereafter, the part 107 is secured to the member 105 and cemented to this member so that it becomes a permanent part of the trip device.

The member 107 is provided to permit adjustment of the tripping device to a limited extent in the field. Referring to FIG. 1, it will be seen that the member 107 is positioned in a cup-shaped opening 141 in the housing parts 9 and 11. A slot 143 is provided in the adjusting member 107 to receive a screwdriver. When it is desired to adjust the trip device, the member 107 is rotated either clockwise or counterclockwise (FIG. 1) rotating the screw 105 to move the bimetal structure 101 to thereby vary the amount of latched engagement between the releasable member 81 and the bimetal structure 101. 7 When the bimetal structure 101 is in the normal position shown in FIG. 2, the part 111 thereof is flexed slightly to the right by means of the screw 105 which biases against the bimetal part 112. Thus, if it is desired to adjust the trip device so that the breaker will trip or upon the occurrence of a greater minimum over-load, the member 107 is rotated counterclockwise (FIG. 1) to move the screw 105 up (FIG. 2) to permit the bimetal structure 101 to unflex to the left. This movement of the bimetal structure 101 increases the amount of latch engagement between the releasable member 81 and the bimetal structure 101 so that the minimum overload current that will trip the breaker will be greater than that prior to this adjustment.

If the adjusting member 107 is rotated clockwise (FIG.

1) the'screw 105 is moved down (FIG. 2) to move the bimetal structure to the right. This movement of the bimetal structure 101 decreases the amount of latch engagement between the releasable member 81 and the bimetal structure 101 so that the minimum overload current that will trip the breaker will be less than that prior to this adjustment. The adjustingmember 107 is limited to rotation of less than 90 in either directiomfrom the position in which it is seen in FIG. 1, by means of stop surfaces 145 thereon that engage with stop surfaces 147 on the housing parts 9 and 11. Thus, the trip mechanism cannot be over adjusted in the field in a manner that would damage the bimetal structure or prevent interruption of the circuit upon the occurrence of a damaging overload.

Two leads 153 and 155 (FIG. 2) from the lamp 19 can be connected across the line in the terminals 31 (FIG. 3) and 65 (FIG. 4) in order to provide a visual indication of whether the circuit controlled by the breaker is closed or opened. A plastic cap 157 is suitably supported on the circuit breaker housing to protect the lamp 19.

A different embodiment of the invention is illustrated in FIG. 6, wherein the reference characters that are similar to the reference characters of the trip structure seen in FIG. 2 are the same as the reference characters of FIG. 2 except that they are primed. As shown in FIG. 6, a bimetal structure 101 comprises a lower bimetal member 111' that latches the end 99 of the releasable member 81 in the same manner as was hereinbefore described, and an upper generally L-shaped bimetal member 112' that is suitably attached to the member 111'. Because the calibrating screw is disposed to the right of the bimetal 111 rather than to the left as seen in FIG. 2, it can be understood that the housing and supporting structures seen in FIG. 2 will be slightly altered to provide adequate spacing for the parts of the trip mechanism 17 seen in FIG. 6. Otherwise, the trip mechanism 17 is used in a circuit breaker almost identical to that shown and described in FIGS. 1-4.

As seen in FIG. 6, the high expansion side of the bimetal 111' is on the left and the high expansion side of the bimetal 112' is to the right and on the lower side of the member 112'. With this disposition of parts, the member 112' serves as a compensating bimetal to compensate for deflection of the part 111 in response to changes in ambient temperature.

As seen in FIG. 6, when there is a rise in ambient temperature, the bimetal 111 of the bimetal structure 101 is heated and it flexes so that the lower or free end thereof moves to the right tending to decrease the amount of latching engagement between the bimetal 111' and the releasable member 81. At the same time, however, the ambient temperature heats the compensating bimetal 112' whereupon this member flexes moving the free end thereof up as seen in FIG. 6 to increase the bias of this member on the screw 105' to .thereby force the lower or free'end of the bimetal 111' back to the left so that there is in effect no change in the amount of latching engagement between the bimetal 111' and the releasable member 81' in response to a rise in ambient temperature. If the ambient temperature then drops, the bimetal 111 will unflex tending to move the free end thereof to the left and the bimetal 112' will unflex to decrease its bias on the screw 105 so that there is in effect no change in latching engagement in response to the drop in ambient temperature. Thus, the bimetal 112' compensates for movement of the bimetal 111 in response to changes in ambient temperature.

When the circuit breaker mechanism 17 is in the normal position, the bimetal part 111 is flexed slightly to the left as seen in FIG. 6. Thus, counterclockwise movement (FIG. 1) of the member 107' moves the screw 105' up to permit the member 111' to unflex so that its free end moves to the right to decrease the amount of latching engagement between the member 81' and the member 111'. Clockwise (FIG. 1) rotation of the member 107' moves the screw 105 down to increase the amount of latching engagement between the releasable member 81' and the member 111'.

From the foregoing, it will be understood that there is provided by this invention a circuit breaker having an improved tripping mechanism that is externally adjustable in the field. In one embodiment of the invention, the adjusting means cooperates with a bimetal .part of an improved bimetal structure to enhance the unlatching or tripping movement of the bimetal structure during a tripping operation of the breaker. In another embodiment, the adjusting means cooperate with a bimetal to compensate for any flexing of a latching bimetal in response to changes in ambient temperature.

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details may .be made without departing from some of the essential features of the invention.

I claim as my invention:

1. A circuit breaker comprising a pair of cooperating 7 contacts, a latched trip member releasable to eifect opening of said contacts, a member stationary during opening operations of said circuit breaker, a bimetal structure comprising a first bimetal part latching said trip member and a flat second bimetal part engaging said stationary member, means heating said bimetal structure in response .to the current flow through the circuit of said circuit breaker, upon the occurrence of a predetermined overload current in said circuit, said bimetal structure being heated and said first bimetal part flexing to move to release said tripmember and said flat second bimetal part flexing and moving a flat side thereof against said stationary member to enhance the releasing movement of said first bimetal part.

2. A circuit breaker comprising a pair of contacts operable to open and close an electric circuit, trip means comprising a flat bimetal member, said bimetal member comprising a flat first part and a flat second part lanced from said flat first part, a latched trip member releasable to effect opening of said contacts, said bimetal member being in an initial position wherein said first part latches said trip member, adjusting means engaging said second part and operable to vary the initial position of said bimetal member, said adjusting means being stationary during opening operations of said circuit breaker, means heating said bimetal member in response to the current flow through said circuit, upon the occurrence of certain over load current conditions in said circuit said first part thermally bending to move to release said trip member and said second part thermally bending and moving a flat side thereof against said adjusting means to increase the releasing movement of said first part.

3. A circuit breaker comprising a pair of cooperating contacts, a latched trip member releasable to effect opening of said contacts, a member stationary during said opening operation, a bimetal structure comprising an elongated first bimetal part latching said trip member and a flat second bimetal part extending generally normal to said first bimetal part, upon the occurrence of a change in ambient temperature said first bimetal part deflecting and said, fiat second bimetal part deflecting and reacting with a flat side side thereof biasing against said stationary member to thereby compensate for said deflection of said first bimetal part, means heating said first bimetal part in response to the current flow through the circuit of said circuit breaker, and upon the occurrence of certain over load current conditions in said circuit said first bimetal part deflecting in the unlatching direction sufficiently to release said trip member.

4 A circuit breaker comprising a pair of contacts separable to open an electric circuit, a latched trip member releasable to efiect opening of said contacts, a trip device comprising a bimetal structure in an initial position to latch said trip member, said bimetal structure comprising an elongated first bimetal part latching said trip member and a flat second bimetal part extending generally normal to said first bimetal part, an adjusting screw engaging a flat side 10f said flat second bimetal part and rotatable to vary said initial position of said bimetal structure, said adjusting screw being stationary during opening operations of said circuit breaker, upon the occurrence of a change in ambient temperature said first bimetal part deflecting and said flat second bimetal part deflecting and reacting with said flat side thereof biasing against said stationary adjusting screw to thereby compensate for said deflection of said first bimetal part, means heating said first bimetal part in response to the current fiow through the circuit of said circuit breaker, and upon the occurrence of certain over load current conditions in said circuit said first part thermally deflecting in the unlatching direction sufliciently to release said trip memher.

5. A circuit breaker comprising a pair of contacts, a latched trip member releasable to efiect opening of said contacts, an adjusting screw stationary during opening operations of said circuit breaker, a flat bimetal structure comprising a flat first elongated bimetal part fixedly supported at one end thereof and having the other end free, said bimetal structure comprising a flat second bimetal part disposed intermediate the ends of said first bimetal part on the high-expansion side of said first bimetal part and extending generally normal to said first bimetal part, said first bimetal part comprising latching means disposed between said second bimetal part and said free end and latching said releasable member, said adjusting screw being disposed onthe flat side of said second bimetal part that is opposite the side that faces the free end of said second bimetal part, means heating said bimetal structure in response to the current flow through the circuit of said circuit breaker, upon the occurrence of certain overload current conditions said first bimetal part deflecting with the free end thereof moving away from said releasable member to an unlatching position to thereby release said releasable member and said second bimetal part deflecting to move said flat side against said adjusting screw to enhance the unlatching movement of said first bimetal part. I

6. A circuit breaker comprising a stationary contact and a movable contact cooperable with said stationary contacts to open and close an electric circuit, a bimetal structure comprising a first flat elongated bimetal part fixedly supported at one end and having the other end free, said bimetal structure comprising a second flat bimetal part disposed intermediate the ends of said first bimetal part on the low expansion side of said first bimetal part and extending generally normal to said first bimetal part, a latched releasable member disposed on the high-expansion side of said first bimetal part, latching means on said first bimetal part between said second bimetal part and the free end of said first bimetal part and latching said releasable member, an adjusting screw stationary during opening operations'of said circuit breaker, said adjusting screw engaging the low-expansion flat side of said second bimetal part between said second bimetal part and the supported end of said first bimetal part, upon a rise in ambient temperature said first bimetal part deflecting away from said releasable member in unlatching direction and said second bimetal part deflecting moving the low-expansion flat side thereof against said adjusting screw to compensate for said unlatching .deflection of said first bimetal part, means heating said first bimetal part in response to the current flow through the circuit of said circuit breaker, and upon the occurrence of overload current conditions above a predetermined amount said first bimetal part deflecting sulficiently to. effect release of said trip member.

References Cited by the Examiner UNITED STATES PATENTS 1,728,785 9/29 Claytor 200'll6 2,340,050 1/44 Gano 200-116 2,872,548 2/59 Christensen 200-139 2,952,757 9/60 Ellenberger 200116 3,038,047 6/62 Marquis 200-,-1l6 3,067,629 12/62 Zurles 74526 BERNARD A. GILHEANY, Primary Examiner. 

1. A CIRCUIT BREAKER COMPRISING A APIR OF COOPERATING CONTACTS, A LATCHED TRIP MEMBER RELEASABLE TO EFFECT OPENING OF SAID CONTACTS, A MEMBER STATIONARY DURING OPENING OPERATIONS OF SAID CIRCUIR BREAKER, A BIMETAL STRUCTURE COMPRISING A FIRST BIMETAL PART LATCHING SAID TRIP MEMBER AND A FLAT SECOND BIMETAL PART ENGAGING SAID STATIONARY MEMBER, MEANS HEATING SAID BIMETAL STRUCTURE IN RESPONSE TO THE CURRENT FLOW THROUGH THE CIRCUIT OF SAID CIRCUIT BREAKER, UPON THE OCCURRENCE OF A PREDETERMINED OVERLOAD CURRENT IN SAID CIRCUIT, SAID BIMETAL STRUCTURE BEING HEATED AND SAID FIRST BIMETAL PART FLEXING TO MOVE TO RELEASE SAID TRIP MEMBER AND SAID FLAT SECOND BIMETAL PART FLEXING AND MOVING A FLAT SIDE THEREOF AGAINST SAID STATIONARY MEMBER TO ENHANCE THE RELEASING MOVEMENT OF SAID FIRST BIMETAL PART. 